Helminthosporoside,a host-specific toxin fromHelminthosporium sacchari: A structure revision and a new partial structure

Summary Reevaluation of the previously proposed structure of helminthosporoside, a host-specific toxin fromHelminthosporium sacchari, reveals a sesquiterpenoid bis-digalactoside. The carbohydrate portion of the toxin was characterized by¹³C-NMR spectroscopy, methylation analyses, FD and FAB mass spectroscopy. The ring size and anomeric configuration of the galactose moieties were determined by utilizing a¹³C-NMR structural analysis method. A new partial structure is proposed.Acknowledgment. We extend special thanks to C.E. Costello, Department of Chemistry, M.I.T., Cambridge, MA, for FD mass spectral analyses, and to C.E. Ballou, Department of Biochemistry, University of California, Berkeley, CA, for FAB mass spectral analyses. We submit sincere appreciation to both V.N. Reihold, Harvard Medical School, Boston, MA, and P. Albersheim, Department of Chemistry, University of Colorado, Boulder, CO, for methylation analyses. We thank J.S. Frye at the Colorado State University Regional NMR-Center, funded by National Science Foundation grant No. DHE 78-18581, Department of Chemistry, Colorado State University, Fort Collins, Co, for high resolution CMR and NMR, and we are grateful to P.W. Jennings, Department of Chemistry, Montana State University, Bozeman, Mt, for total carbon analyses. This work was supported in part by a Herman Frasch Foundation grant to G.A. Strobel, by NSF grant PCM-78-22517, and funds from the Montana Agricultural Experiment Station. B.P. Mundy acknowledges the partial support of NSF (ISP-801149).     

Stimulation of bone resorption and inhibition of bone formation in vitro by human tumour necrosis factors

When leukocytes are exposed to mitogens or antigens in vitro, they release bone-resorbing activity into the culture supernatants which can be detected by bioassay. Like many lymphocyte-monocyte products, this activity has been difficult to purify because of its low abundance in activated leukocyte cultures and the unwieldy bioassay required to detect biological activity. Partially purified preparations of this activity inhibit bone collagen synthesis in organ cultures of fetal rat calvariae. Recent data suggest that both activated lymphocytes and monocytes release factors which could contribute to this activity. Recently, monocyte-derived tumour necrosis factor alpha (TNF-alpha) and lymphocyte-derived tumour necrosis factor beta (TNF-beta) (previously called lymphotoxin), two multifunctional cytokines which have similar cytotoxic effects on neoplastic cell lines, have been purified to homogeneity and their complementary DNAs cloned and expressed in Escherichia coli. As both of these cytokines are likely to be present in activated leukocyte supernatants, we tested purified recombinant preparations for their effects on bone resorption and bone collagen synthesis in vitro, and report here that both cytokines at 10(-7) to 10(-9) M caused osteoclastic bone resorption and inhibited bone collagen synthesis. These data suggest that at least part of the bone-resorbing activity present in activated leukocyte culture supernatants may be due to these cytokines.     

Bone metastasis: can osteoclasts be excluded?

The RANK/RANKL signalling mechanism is the final common pathway of osteoclast formation and activity. Inhibitors of RANK ligand (RANKL) that bind to RANK (for 'receptor activator of NF-kappaB'), such as osteoprotegerin (OPG), neutralizing antibodies against RANKL and soluble RANK antagonists, are well described inhibitors of bone metastasis in preclinical and clinical models, presumably because of their effects on osteoclasts. Jones et al. show that OPG inhibits bone metastasis after intracardiac injection of B16F10 murine melanoma cells, but claim that bone metastases are entirely independent of osteoclast formation and bone resorption: rather, they are caused by an effect on cell migration through RANK. However, we question whether these surprising conclusions are rigorously supported by their data.